National Animal Health Diagnostic and Investigation Center, P. O. Box 04, Sebeta, Ethiopia.
Aklilu Lemma Institute of Pathobiology, Addis Ababa University, P. O. Box 1176, Addis Ababa, Ethiopia.
BMC Vet Res. 2019 Jul 26;15(1):262. doi: 10.1186/s12917-019-1962-1.
Dairy cattle movement could be a major risk factor for the spread of bovine tuberculosis (BTB) in emerging dairy belts of Ethiopia. Dairy cattle may be moved between farms over long distances, and hence understanding the route and frequency of the movements is essential to establish the pattern of spread of BTB between farms, which could ultimately help to inform policy makers to design cost effective control strategies. The objective of this study was, therefore, to investigate the network structure of dairy cattle movement and its influence on the transmission and prevalence of BTB in three emerging areas among the Ethiopian dairy belts, namely the cities of Hawassa, Gondar and Mekelle.
A questionnaire survey was conducted in 278 farms to collect data on the pattern of dairy cattle movement for the last 5 years (September 2013 to August 2018). Visualization of the network structure and analysis of the relationship between the network patterns and the prevalence of BTB in these regions were made using social network analysis.
The cattle movement network structure display both scale free and small world properties implying local clustering with fewer farms being highly connected, at higher risk of infection, with the potential to act as super spreaders of BTB if infected. Farms having a history of cattle movements onto the herds were more likely to be affected by BTB (OR: 2.2) compared to farms not having a link history. Euclidean distance between farms and the batch size of animals moved on were positively correlated with prevalence of BTB. On the other hand, farms having one or more outgoing cattle showed a decrease on the likelihood of BTB infection (OR = 0.57) compared to farms which maintained their cattle.
This study showed that the patterns of cattle movement and size of animal moved between farms contributed to the potential for BTB transmission. The few farms with the bulk of transmission potential could be efficiently targeted by control measures aimed at reducing the spread of BTB. The network structure described can also provide the starting point to build and estimate dynamic transmission models for BTB, and other infectious diseases.
奶牛的移动可能是埃塞俄比亚新兴奶牛带中牛结核病（BTB）传播的一个主要风险因素。奶牛可能会在农场之间长距离移动，因此了解移动的路线和频率对于确定农场之间 BTB 的传播模式至关重要，这最终有助于为决策者提供信息，以制定具有成本效益的控制策略。因此，本研究的目的是调查奶牛移动的网络结构及其对三个埃塞俄比亚奶牛带新兴地区（Hawassa、Gondar 和 Mekelle 市）之间 BTB 传播和流行的影响。
对 278 个农场进行了问卷调查，以收集过去 5 年（2013 年 9 月至 2018 年 8 月）奶牛移动模式的数据。使用社会网络分析对网络结构进行可视化，并分析这些地区网络模式与 BTB 流行之间的关系。
奶牛移动网络结构显示出具有无标度和小世界特性，意味着存在局部聚类，少数农场的连接度较高，感染风险较高，如果感染，可能成为 BTB 的超级传播者。与没有联系历史的农场相比，有奶牛移动到畜群历史的农场更有可能受到 BTB 的影响（OR：2.2）。农场之间的欧几里得距离和移动的动物批次大小与 BTB 的流行呈正相关。另一方面，与保持其牛群的农场相比，有一头或多头外出牛的农场 BTB 感染的可能性降低（OR=0.57）。
本研究表明，牛群移动的模式和农场之间动物移动的规模促成了 BTB 传播的潜力。少数具有大量传播潜力的农场可以通过旨在减少 BTB 传播的控制措施有效地作为目标。所描述的网络结构还可以为构建和估计 BTB 和其他传染病的动态传播模型提供起点。
